In various types of fuel cell stacks, whether anode and cathode water management is active (employing a pump) or passive (no pump) the stack is cooled by cooler plates which are separated by groups of fuel cells. In some fuel cell system designs, there may be as few as two fuel cells between successive cooler plates. Because the cooler plates do not contribute to the voltage or power of a fuel cell stack, the power density of the fuel cell system and end-to-end voltage of the stack correlate inversely with the number of cooler plates which are used in the stack. The overall size of the fuel cell stack becomes critical in fuel cells designed for automotive use.
If more fuel cells are interposed between successive cooler plates, the fuel cells further away from the cooler plates, particularly at the centers of said fuel cells, experience higher temperatures, which impacts overall fuel cell stack water balance, and reduces life in membranes or other temperature sensitive components. Overall stack water balance depends on the exit temperature of the oxidant, due to the impact on partial pressure of water vapor leaving the stack in the oxidant outflow, and on the overall oxidant utilization of the stack.